<form>
    <div class="row">
        <form class="col s12">
          <div class="row">

            <div class="input-field col s12">
              <i class="material-icons prefix">account_circle</i>
              <input id="login_username" type="text" class="validate" >
              <label for="login_username">用户名</label>
            </div>
            <br>
            <div class="input-field col s12">
              <i class="material-icons prefix">lock_outline</i>
              <input id="login_password" type="password" class="validate">
              <label for="login_password">密码</label>
            </div>
          </div>
        </form>
      </div>

</form>